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Unformatted text preview: Chapter 9 Natural Convection 942 A cylindrical propane tank is exposed to calm ambient air. The propane is slowly vaporized due to a crack developed at the top of the tank. The time it will take for the tank to empty is to be determined. Assumptions 1 Steady operating conditions exist. 2 Air is an ideal gas with constant properties. 3 The local atmospheric pressure is 1 atm. 4 Radiation heat transfer is negligible. D = 1.5 m L = 4 m Propane tank ε ≈ 0 T s = 42 ° C Air T ∞ = 25 ° C Properties The properties of air at 1 atm and the film temperature of ( T s + T ∞ )/2 = (42+25)/2 = 8.5 ° C are (Table A15) 1 2 5 K 003781 . K ) 273 5 . 8 ( 1 1 7383 . Pr /s m 10 265 . 1 C W/m. 02299 . = + − = = = × = ° = − f T k β υ Analysis The tank gains heat through its cylindrical surface as well as its circular end surfaces. For convenience, we take the heat transfer coefficient at the end surfaces of the tank to be the same as that of its side surface. (The alternative is to treat the end surfaces as a vertical plate, but this will double the amount side surface....
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This note was uploaded on 01/24/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.
 Fall '10
 Dr.DanielArenas
 Thermodynamics, Convection, Mass

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